Patent GB-294351-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/58
Filed: 1927-06-18
Abstract: 294,351. Automatic Telephone Manufacturing Co., Ltd., and Taylor, R. June 18, 1927. No Patent granted (Sealing fee not paid). Automatic exchange systems.- After a junction from a satellite to a main exchange has been opened by the calling subscriber's disconnection or otherwise, it is kept guarded during the release periods of two slow relays, so as to give ample time for the release of a register-controller at the main exchange. When the calling subscriber disconnects himself after conversation the junction is guarded during the release of relays B, BB; if he gets a busy signal and disconnects himself during a lamp-flash period the junction is guarded until the lamp-flash period is over and then during the release of MD, BB; if the call proves to be local or to a near-by exchange directly accessible the junction is disconnected and is guarded during the release of LZ, LD. A call by a satellite subscriber is extended to a selector-repeater SR, Fig. 1, which acts as a group selector for local and near-by calls and as a repeater for main-exchange calls, the latter being completed over a junction seized by a switch RLS. Local, near-by and main-exchange calls are distinguished by a 3-digit discriminating relay set DRS, Fig. 2, which is operated over terminals 121 - - 130 by a fourth wiper 101 of the selector-repeater. A simplified form of discriminator can be used with the selector-repeater in areas not using register-controllers. Specifications 162,297, 174,332, 196,245 and 210,733 are referred to. Seizure of junction to main exchange. On energization of the relays A, B, BB a circuit is closed for magnet DM (93, 61, 80, 104, 60, 79, 42) which drives the switch RLS off normal and continues to be energized over the wiper 104 until an idle junction is found, whereupon the switching relay K and relays LZ, MD are energized and a lamp 16 is lit. The junction is busied over 104, 69, 42, and also over 80, 61, 94, 60, 79, 42. If all junctions are busy the switch RLS goes to its last contacts, closing a motor start circuit 77 and connecting up dialling tone (which is normally sent back from the main exchange) from wire 114. If subsequently it proves that the main exchange is wanted, relay JD is energized and replaces the dialling tone by busy tone from wire 75. Discrimination of local and other calls. Calls to a near-by exchange have a prefix 334 or 805, and go over the 4th or 5th level of the selectorrepeater, which is not released after the final digit of the prefix; local calls have a prefix 205 or 436, the selector-repeater being released after the final digit of the prefix and the call being extended over a level (excluding the 4th and 5th) determined by the next digit; in both these cases relay LD is energized and conditions the selector for hunting, so that eventually the call is switched by relay H through the wipers 98, 99. the junction being released; calls to the main exchange may have any other prefix (including zero calls) and after 1, 2 or 3 digits, as soon as it is determined that the main exchange is wanted, relay JD is energized and brings the discriminating operations to an end. The prefix digits are repeated to the vertical magnet V and to the junction 106, 107. During each digit, relay G is energized over 55, 90, 67, 35 and at its termination the rotary magnet R is energized to bring the grounded discriminating wiper 101 on to one of the contacts 121 - - 130, Fig. 2, but hunting does not take place because the connection of the stepping relay G to the test wiper 100 is open at 82, 83. Assuming first that the call has the local prefix 436, the first digit 4 energizes relay AB (over 124, 186) which locks up and closes a, circuit 110 for the release magnet Z, and on the return of the selector-repeater to normal a circuit is closed to energize relay OA, which locks up and opens the release circuit. The second digit 3 energizes BA (over 123, 189, 179, 173, 141) which locks up and again energizes the release magnet Z, and circuit 111 is then again closed to energize OB, which locks up and opens the release circuit. The third digit 6 energizes CA (over 126, 170, 150) which locks up and again energizes Z, and LD is then energized over 111, 148, 113. Relay LD locks itself, keeps the junction busy over 81, and unlocks K, which disconnects the junction and unlocks LZ, which opens one of two parallel contacts in the locking circuit of LD. After the next digit, the selector-repeater hunts by interaction of G and R (since contacts 82, 83 are now closed) until an idle local selector is found, whereupon H is energized, switches through to the wipers 98, 99, disconnects the magnet V, and opens the second parallel contact of the locking circuit of LD, which falls back and removes guarding potential from the wiper 104. Thus the junction is guarded after its release for at least the combined periods of LZ, LD. Assuming nexb that the call is to a near-by exchange with prefix 334, the first digit energizes AA, OA, the second digit energizes BA, OB (the release magnet Z being energized after each of these digits) and the third digit directly energizes LD (over 124, 187, 178, 152, 113) so that the selector-repeater is not released but proceeds to hunt at once on its 4th level. Assuming, lastly, that the call is to the main exchange with prefix 335, the third digit 5 directly energizes relay JD (over 125, 165, 158, 115) and JD is likewise energized by any other prefix not reserved to local or near-by calls, for example a first digit 1, 5, 6, 7, 9 or 0 would energize it immediately. The relay JD locks itself, unlocks LZ, and disconnects the magnet V, so that further digits take effect only at the main exchange. The junction remains busied over 104, 80, 61, 94, 60, 79, 42. Metering. The energization of relay D, when the called subscriber answers, de-energizes MD; the meter is operated over 38, 59 (or 78), 45 and the lamp 16 is extinguished. Release. Relays A, B, BB relapse successively, and ground is taken off the wire 13 at 44 and off wiper 104 (in the case of a main-exchange call, at 42. If the calling subscriber disconnects while battery is connected to the outgoing b wire (which may be due to busy flash currents or to operatorhold conditions) relay I is energized over 28, 48 and keeps MD, BB energized until battery is disconnected from the b wire. The release magnet Z is energized and K unlocked on the relapse of BB, and a homing circuit for the switch RLS is closed over 92, 105, 41. If the called subscriber is the first to disconnect himself the lamp 16 is lit over 37, 59 (or 78), 45.